HEAT TREATMENT OF CHOPPED ALFALFA IN ROTARY DRUM DRYERS

This paper deals with the heat treatment of alfalfa chops during the high temperature dehydration process. It outlines the dryer characteristics, difficulties and potential errors in measuring temperatures in the dryer, computation techniques, the relationships between moisture and temperature during drying, and the potential effect of dehydration on the destruction of the insect Hessian Fly due to elevated temperatures.

From the analysis based on an existing computer model for dehydration of alfalfa chops, and the available field data, it is shown that the dried chops will attain a temperature of 90°C or higher when the input temperatures are between 500°C and 800°C. These conditions apply to the drying of wet alfalfa (moisture content more than 55 percent wet basis). The plant material loses a large portion of its moisture in the first few seconds in the dryer. The rapid release of moisture may cause the rupture or detachment of particles such as eggs, larva, pupa, and insects from the plant material. These small particles are exposed to an intense heat and rapid dehydration.     

CORRELATIONS FOR THE EQUILIBRIUM MOISTURE CONTENT OF SOI.IDS

Water adsorption and desorption isotherms at various temperatures have been generated for a variety of particulate materials (ion exchange resin, silica gel, wheat and cellulose materials). Most of thc data were obraincd with the SPS Equilibrium Moisture Content rig, using a dynamic equilibration method. Equilibration over saturated salt solutions at 2°C (static method) was also used for some of the data. Seven semi-empitical correlations, available in the literature, and one developed by SPS have been used to relate the equilibrium moisture content of the material to the relative humidity and temperature of the air. These equations enable the equilibrium moisture content to be predicted under various conditions of relative humidity and temperature from a small number of tests. For each of the six materials tested at least one of the correlations gave a good fit. However, there was no correlation which predicted the equilibrium moisnrre content well for every one of the six materials.     

THE DESIGN OF FLIGHTS IN CASCADING ROTARY DRYERS

ABSTRACT

In designing cascading rotary dryers, it is important to size the flights correctly in order to ensure....     

SIMULATION AND SCALE-UP OF PNEUMATIC CONVEYING AND CASCADING ROTARY DRYERS

ABSTRACT

This paper presents a unified model for simulation of cocurrent and countercurrent dispersion-type dryers. The main industrial applications are to pneumatic conveying (flash) dryers and cascading (direct) rotary dryers. The basic model is a one-dimensional incremental (stepwise) simulation, which has been developed over a number of years Equations for particle motion, heat and mass transfer, heat and mass balances and local gas conditions are solved simultaneously over a small increment along the dryer. All workers have previously had considerable difficulty in obtaining a good fit between simulations and actual results from pilot-plants or large-scale industrial dryers. A new “fitting mode” calculation overcomes this by identifying the parameters which need to be adjusted, concentrating on those which cannot be measured accurately. Excellent agreement has been obtained between the model and experimental data by this method. The paper also presents revised formulations for particle motion and heat transfer in rotary dryers. The model has been incorporated into two computer programs for flash and rotary dryers respectively, and results from the former are shown for a case study.     

THE DESIGN OF FLIGHTS IN CASCADING ROTARY DRYERS

In designing cascading rotary dryers, it is important to size the flights correctly in order to ensure that they can adequately accommodate the contents of the drum. A set of equations has been derived to calculate the solids holdup on angular and extended-circular flights in such dryers. Three examples of the practical use of these equations are presented. These include estimation of the design holdup of the dryer, selection of the number of flights, and exploration of the flight cascade characteristics.     

THE DESIGN OF FLIGHTS IN CASCADING ROTARY DRYERS

ABSTRACT

In designing cascading rotary dryers, it is important to size the flights correctly in order to ensure....     

THE DESIGN OF FLIGHTS IN CASCADING ROTARY DRYERS

ABSTRACT

In designing cascading rotary dryers, it is important to size the flights correctly in order to ensure.…     

THE DESIGN OF FLIGHTS IN CASCADING ROTARY DRYERS

ABSTRACT

In designing cascading rotary dryers, it is important to size the flights correctly in order to ensure.…     

SIMULATION AND SCALE-UP OF PNEUMATIC CONVEYING AND CASCADING ROTARY DRYERS

This paper presents a unified model for simulation of cocurrent and countercurrent dispersion-type dryers. The main industrial applications are to pneumatic conveying (flash) dryers and cascading (direct) rotary dryers. The basic model is a one-dimensional incremental (stepwise) simulation, which has been developed over a number of years Equations for particle motion, heat and mass transfer, heat and mass balances and local gas conditions are solved simultaneously over a small increment along the dryer. All workers have previously had considerable difficulty in obtaining a good fit between simulations and actual results from pilot-plants or large-scale industrial dryers. A new “fitting mode” calculation overcomes this by identifying the parameters which need to be adjusted, concentrating on those which cannot be measured accurately. Excellent agreement has been obtained between the model and experimental data by this method. The paper also presents revised formulations for particle motion and heat transfer in rotary dryers. The model has been incorporated into two computer programs for flash and rotary dryers respectively, and results from the former are shown for a case study.     

EFFECT OF PARTICLE CASCADE FROM FLIGHTS ON HEAT TRANSFER AND PRESSURE DROP IN ROTARY DRYERS AND COOLERS

It is shown that in small laboratory rotary dryers and coolers particles fall discontinuously from flights in the regime where a relatively small number of particles fall from flights and that particles fall continuously from flights forming multiple cascading layers in the regime of a relatively large number of falling particles. The correction factor for the gas-to-particle heat transfer coefficient estimated by the Ranz-Marshall equation is about 1 in the former case and takes on values lower than 1 in the latter     

RESIDENCE TIMES OF TWO- AND THREE-COMPONENT MIXTURES IN CASCADING ROTARY DRYERS

The residence times of the components of two- and three-component mixtures of fine (195 µm), coarse (1315 µm) and very coarse (5040 µm) sands were measured in a pilot-scale cascading rotary dryer. The effects of mixture composition and air velocity (0-5.4 m s^-1) were determined. With no air flowing through the drum, the residence times of the individual components were almost the same as that of the overall mixture. Increasing the gas velocity caused a large decrease in residence time. In contrast, particle size had very little effect. The spread of residence times increased with air velocity, peaking between 2 and 4 m s^-1; composition had very little effect on the spread. The residence time of the overall mixture could be calculated using the particle transport model of Matchett and Baker if both the modified drag coefficient Φ_d and the particle Reynolds number Re_p were based on the superficial air velocity and the mass-average particle diameter.     

ADSORPTION DRYING OF CORN IN ZEOLITE GRANULES USING A ROTARY DRUM

ABSTRACT

This study was conducted to evaluate the potential of a natural zeolite (chabazite) as the particulate medium for grain drying. The granular zeolite was heated in an electric oven and mixed with grain corn. Drying experiments were conducted in a rotary batch dryer equipped with a computer and a data acquisition and control unit simulating an adiabatic process. Five initial medium temperatures (140, 160, 180, 200, and 220 °C) were used. Drying curves for grain corn and the values of effective diffusivity are reported. The amount of moisture removed and     

BOOKS RECEIVED

As a result of modifications of BET model assumptions a new equation for sorption/desorption isotherms containing three constants was obtained. The proposed equation was verified successfully by means of measurements of sorption and desorption isotherms of water vapour for 29 substances and low-temperature adsorption of argon on 10 materials. Our own equation fits better, sometimes even much better, to the experimental points than the relations proposed by Harkins and Jura. Kühn, Halsey, Henderson, and Brunauer. Emmett and Teller (n = ∞).     

SCALE-UP OF LAYER DRYERS: A UNIFIED APPROACH

Abstract

The concept of Specific Drying Rate is introduced for analysis of experimental drying data for layer dryers and as a convenient scale-up factor. In conjunction with data obtained from a batch laboratory simulation the method is applicable to most types of continuous layer dryers. Three illustrations of the use of this approach for scale-up are presented including a continuous convection heated rotary shelf dryer, an indirectly heated paddle dryer, and an indirectly heated plate dryer with heating zones.     

转盘滤池在污水处理厂深度处理中的应用实践

为提升出水水质,郑州市五龙口污水处理厂(一期)工程在原有工艺的基础上,对原先设计为直接排放的5×104m3/d二级出水增加以转盘滤池为主体的深度处理工艺设施。实际运行结果表明,以转盘滤池为主体的深度处理工艺出水水质超出设计标准城镇污水处理厂污染物排放标准(GB 18918-2002)一级B标准,达到一级A标准,运行效果良好、稳定可靠。     

二氧化碳压缩机低压缸振动故障的分析与处理

针对二氧化碳压缩机低压缸振动现象进行分析,提出相应的检修处理方案和具体的防范措施.     

高温热处理对PI基炭薄膜的影响

研究了在氩气气氛的保护下,PI（聚酰亚胺）基炭薄膜在高温热处理过程中结构转变的过程和试样的若干性能与热处理温度的关系。用激光拉曼光谱和X—射线衍射技术对其样品的结构参数给予了表征。实验表明,在1700℃以前样品纵、横方向处于收缩状态,1700℃至3160℃（终温）则处于伸长状态;而重量变化却在2100℃以前处于减小状态,2100℃以后呈增重状态;电导率由1．03×102S／cm（1000℃）增加到2．1×104S／cm（3160℃）。随着热处理温度的提高．样品表面结构的有序度增加,终温样品十分接近石墨晶体;样品结构参数d002值逐渐减小,Lc值却一直处于增加状态。     

热处理制度对微晶泡沫玻璃性能的影响

以粉煤灰为主要原料,用CaCO3作为发泡剂,Na3PO4·12H2O作为稳泡剂,制备出了性能优良微晶泡沫玻璃。研究了发泡温度、发泡时间等因素对微晶泡沫玻璃性能的影响。结果表明,随着发泡温度的升高和保温时间的增加,体积密度均先减小后增大,最佳发泡温度1025℃,发泡时间30min。析出的晶体有钙长石CaAl2Si2O8、普通辉石Ca(Mg,Fe,Al)(Si,Al)2O6;密度为1.02g.cm-3;热膨胀系数为7.51×10-6/℃;抗压强度为19.2MPa;抗弯强度为16.3MPa。     

由干湿球温度计算相对湿度的简捷法

通过对相对湿度与干湿球温度间数据的分析,推导出了由干湿球温度计算相对湿度的两个数学公式,计算中不需查阅水蒸气数据表和试差,准确度较高,适于工程计算。在相对湿度≥４０％,湿球温度０～８０℃,风速＞５ｍ／ｓ的空气—水蒸气系统,平均相对误差为１．７％和１．１％。     

非生产环节中化肥质量的控制

叙述化肥非生产环节即移运,包装,储存等过程的质量控制问题,介绍影响化肥物理质量的关键因素临界相对湿度的概念,分析结块,起尘,流动性差及过度吸湿等化肥物性衰减的原因。